1. Field of the Invention
The present invention relates to an aluminum plating material for anodizing, and an anodized material used for particularly, a colored medium and an antiwear material.
2. Description of the Related Art
Anodizing of aluminum or an aluminum alloy in an electrolytic solution such nitric acid, sulfuric acid, or chromic acid is known to those skilled in the art. An application of an anodized film for, e.g., aircraft, automobile, and optical components is also known. Various types of tools utilizing antiwear properties of hard anodized films are further known.
The present inventors have made extensive studies for a variety of applications of anodized materials which are produced by steps of plating a substrate of a metal except for aluminum or an aluminum alloy, a ceramic substrate, or a plastic substrate with aluminum or an aluminum alloy, and anodizing the plated aluminum film. The present inventors assume that an anodizing reaction of an Al film progresses in accordance with the following mechanism.
______________________________________ Al dissolution: Al .fwdarw. Al.sup.3+, Al.sup.3+ + H.sub.2 O .fwdarw. Al(OH).sub.3 .fwdarw. Al.sub.2 O.sub.3.H.s ub.2 O Anionic discharge and Al.sub.2 O.sub.3 Production: 20H.sup.- .fwdarw. H.sub.2 O + O (nascent oxygen atom) Al + O .fwdarw. Al.sub.2 O.sub.3 (insulating film) ______________________________________
According to the studies of the present inventors, when a composite substrate obtained by directly aluminum-plating a metal substrate except for an aluminum or aluminum alloy substrate is anodized, dissolution of aluminum layer progresses. At the same time, the metal substrate is locally dissolved to result in an anodized aluminum film having nonuniform pores. In particular, when a metal substrate has low resistance to chemicals, it is found that an interface between the substrate and the aluminum layer is undesirably dissolved, and the resultant anodized film may peel from the substrate.
When a composite substrate obtained by directly aluminum-plating a nonconductive plastic or ceramic substrate is anodized, it is found that the anodized film tends to peel from the substrate if adhesion strength between the nonconductive substrate and the aluminum plating layer is low. In addition, since the material becomes insulative as a whole upon anodizing, coloring by electrolysis or electrolysis in pores cannot be performed.